Nitrogen (N) deposition has
doubled the natural N inputs received by ecosystems through biological
N-fixation and is currently a global problem that is affecting the
Mediterranean regions. We evaluated the existing relationships between
increased atmospheric N deposition and biogeochemical indicators related to
soil chemical factors and cryptogam species across semiarid central, southern
and eastern Spain. The cryptogam species studied were the biocrust-forming Pleurochaete squarrosa (moss) and Cladonia foliacea (lichen). Sampling
sites were chosen in Quercus coccifera
(kermes oak) shrublands and Pinus
halepensis (Aleppo pine) forests to cover a range of inorganic N deposition
representative of the levels found in the Iberian Peninsula (between 4.4 and
8.1 kg N ha-1 yr-1). We extended the ambient N deposition
gradient by including experimental plots to which N had been added for three
years at rates of 10, 20 and 50 kg N ha-1 yr-1. Overall,
N deposition (extant plus simulated) increased soil inorganic N availability
and caused soil acidification. Nitrogen deposition increased
phosphomonoesterase (PME) enzyme activity and PME:nitrate reductase (NR) ratio
in both species, whereas the NR activity was reduced only in the moss.
Responses of PME and NR activities were attributed to an induced N to
phosphorus imbalance and to N saturation, respectively. When only considering
the ambient N deposition, soil organic C and N contents were positively related
to N deposition, a response driven by pine forests. The PME:NR ratios of the
moss were better predictors of N deposition rates than PME or NR activities
alone in shrublands, whereas no correlation between N deposition and the lichen
physiology was observed. We conclude that integrative physiological
measurements, such as PME:NR ratios, measured on sensitive species such as P. squarrosa, can provide useful data
for national-scale biomonitoring programs, whereas soil acidification and soil
C and N storage could be useful as additional corroborating ecosystem
indicators of chronic N pollution.

View of Cladonia foliacea, one of the species used in this study. Photograph by Jordi Badia.

1. Drylands cover about 41% of Earth’s land surface, and 65% of their area supports domestic livestock that depends on
the aboveground net primary productivity (ANPP) of natural vegetation. Thus,
understanding how biotic and abiotic factors control ANPP and related ecosystem
functions can largely help to create more sustainable
land use practices in rangelands, particularly in the context of ongoing
global environmental change.

2. We used 311
sites across a broad natural gradient in Patagonian rangelands to evaluate the
relative importance of climate (temperature and precipitation) and vegetation
structure (grass/shrub cover and species richness) as drivers of ANPP,
precipitation-use efficiency (PUE) and precipitation marginal response (PMR).

3. Climatic
variables explained 60%, 52% and 12% of the variation found in grass cover, shrub cover and
species richness, respectively. Shrub cover increased in areas with warmer, drier, and winter rainfall climates while
the response observed for both grass cover and species richness was the
opposite. Climate and vegetation structure explained 70%, 60% and 29% of the variation found
in ANPP, PUE and PMR, respectively. These three variables increased with
increases in vegetation cover, particularly grass cover. Species richness also had a positive effect on ANPP, PUE and
PMR. ANPP increased, and PUE decreased with increasing
mean annual precipitation, whereas PMR increased with increases in the proportion
of precipitation falling in spring-summer.Temperature had a strong negative effect on ANPP and
PUE, and a positive direct effect on PMR. Standardized total effects from
structural equation modelling showed that vegetation structure and climate had similar
strengths as drivers of ecosystem
functioning. Grass cover had the highest total effect on ANPP (0.58), PUE
(0.55) and PMR (0.41). Among the climatic variables, mean annual precipitation
had the strongest total effect on ANPP (0.51) and PUE (-0.41), and the
proportion of the precipitation falling in spring-summer was the most
influential on PMR (0.36).

4. Synthesis.Results show that vegetation structure is as
important as climate in shaping ecosystem functioning Patagonian
rangelands. Maintaining
and enhancing vegetation cover and species richness, particularly of grasses
could reduce the adverse effects of climate change on ecosystem functioning in
these ecosystems.

Location of sampling sites
in Patagonia (black dots), with some examples of the vegetation types studied.

Understanding how organisms control soil water
dynamics is a major research goal in dryland ecology. While previous studies have mostly focused on the role of vascular
plants on the hydrological cycle of drylands, recent studies highlighted the
importance of biological soil crusts formed by lichens, mosses and
cyanobacteria (biocrusts) as a major player in this cycle. We used data from a 6.5-year study to evaluate how
multiple abiotic (rainfall characteristics, temperature, and initial soil
moisture) and biotic (vascular plants and biocrusts) factors interact to
determine wetting and drying processes in a semi-arid grassland from Central
Spain. We found that the shrub Retama
sphaerocarpa and biocrusts with medium cover (25-75%) enhanced water gain
and slowed down drying compared with bare ground areas (BSCl). Well-developed
biocrusts (> 75% cover) gained more water, but lost it faster than BSCl microsites.
The grass Stipa tenacissima reduced
infiltration, but increased soil moisture retention compared to BSCl
microsites. Biotic modulation of water dynamics was the result of different
mechanisms acting in tandem and often in opposite directions. For instance,
biocrusts promoted an exponential behaviour during the first stage of the
drying curve, but reduced the importance of soil characteristics that accentuate
drying rates. Biocrust-dominated microsites gained a similar amount of water
than vascular plants, albeit they showed faster water losses than vascular
plants during dry periods. Our results emphasize the importance of biocrusts
for water dynamics in drylands, and illustrate the potential mechanisms behind
their effects. They will help to further advance theoretical and modelling
efforts on the hydrology of drylands and their response to ongoing climate
change.

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We are looking for a motivated candidate to apply to a competitive call from the Regional Government of Madrid for funding a 4-yr post-doctoral contract to work in our lab. The requeriments of the candidates are the following:

* Strong publication record in any of the areas related to the research we do in the lab (for details about we do and recent publications check our webpage). We are particularly interested in candidates with expertise in microbial ecology, bioinformatics or remote sensing.* The candidate should hold a PhD awarded between 1 January 2013 and 20 June 2016* The candidate should have been working (under a contract or fellowship, proof required) outside Spain for at least one of the last two years.

Please note that this is not a job offer, as the candidate will apply to a competitive call (a total of 25 contracts will be awarded for all knowledge areas). All the details of this call (in Spanish) can be found here. If awarded, the person would work in the Dryland Ecology…

We are looking for a motivated candidate to apply to a competitive postdoctoral call ("Juan de la Cierva formación") from the Spanish Government that fully fund a 2-yr postdoctoral contract to work in in the Dryland Ecology and Global Change Lab. The requeriments of the candidate are the following:

* We are particularly interested in candidates with expertise in any of the following areas: microbial ecology, bioinformatics, lichen taxonomy, biocrust ecology, remote sensing or ecological modelling.* The candidate should hold a PhD awarded between 1 January 2015 and 31 December 2016.* The candidate should have a strong publication record, with articles in journals included in the first quartile of the JCR database (the call is highly competitive and succesfull candidates are those with a strong publication record).* Previous research stays and/or postdoctoral experience outside Spain (for Spanish candidates) or a Phd from a non-Spanish university (for candidates from outside Sp…